Brewing for Flavor: Malt
Every time you order a beer, you have certain expectations. Picture yourself perusing the beer menu at a new brewpub. Stout, porter, amber ale, pale ale, weizen, lager. Each of those names creates an image in your mind. That’s what beer styles are all about: creating a standard that tells the consumer—you—what to expect (within a certain range) when you place an order.
An important component of a style is the beer’s flavor. Flavor is a perception that arises from color, aroma, taste, texture, and previous experience. A good beer balances each of these attributes.
Malt-derived flavors find their way into beer when they are extracted during mashing or steeping. Many of the flavors in malt originate during the kilning step of the malting process.
There are four major flavor attributes provided by brewer’s malt:
- Aroma: Dimethyl sulfide (cooked corn aroma) and Maillard Reaction products (toasty, caramel, and roasted aromas)
- Taste: Maillard Reaction products (toasty, roasted, acidic, and burnt tastes)
- Color: Maillard Reaction products (light amber to black colors)
- Texture: Astringency from tannins in the husk (palate-drying and puckering sensations)
In the Beginning
Malt is made by first soaking the barley to get it to sprout. The wet barley is then germinated under controlled conditions, which degrades some of the starch and protein into sugar and amino acids.
Kilning dries and partially cooks (browns) the malt. The early stages of browning form colorless compounds that affect the flavor. Color changes occur during the second phase of the browning process. This second phase is also where all of the aroma compounds arise.
Maillard Reaction
When you cook foods in a certain way, they often pick up similar flavor attributes. That’s true even if the basic tastes of the foods are completely different; the flavor comes from the way they are prepared. Cooking on a barbecue, for instance, gives food a certain smoky flavor—whether you’re cooking corn or hamburgers.
Maillard Reaction refers to just such a phenomenon. Maillard Reactions occur when you brown foods, such as toasting bread or grilling steak. The process gets its name from a French chemist who in 1911 defined the reactions between amino acids and sugars when they are heated. When brewer’s malt is kilned (this is done by the malthouse before you buy it), this reaction takes place.
The trick for the maltster is to brown each type of malt to the perfect point to bring out the desired flavors. Think about cooking toast in a toaster oven. It starts out light and becomes progressively darker. If you take the toast out of the oven during the “light” phase, it will have a different flavor than if you remove it when it’s well browned.
Also, there’s a point at which the toast goes from brown to charred, and it happens quickly. One minute it’s toasting along nicely. You turn your back for a few moments, and by the time you smell the aroma and make it over to the toaster, your toast is black as Guinness!
Since browning begins with different combinations of amino acids and sugars, the process yields many different flavors. In fact, most of the flavors found in malt come from this browning process. They range from slightly toasty and biscuity through toffee and caramel, all the way to roast and burnt. More than 400 browning reaction products have been identified, though they don’t all have unique flavors.
Specialty malts are difficult to make because of the complexity of browning; if the temperature is a little too high or held hot a little too long, then the malt has the wrong color, aroma, and taste. It is tricky to hold something at the edge of burning without actually burning it.
Browning Flavors
Lightly colored malts:
Pale, Munich, Amber, Aromatic
These malts are lightly kilned to preserve enzyme activity. Some of these malts are known as “high kilned” because they are heated to slightly higher temperatures than pale malts. Lightly kilned malts contain products from the early stages of browning that lend biscuity and toasty aromas plus a slight color.
Caramel malts:
Carastan, Caramel, Crystal
Caramel malts are made using a “saccharification rest” after germination and prior to kilning. The moist malt coming out of germination is held near 158˚ F during the saccharification rest, allowing for mashing to occur in each individual malt kernel. This yields many sugars that can react in the browning process.
The result is an increase in the variety of flavors produced during kilning. Typical aromas are caramel, burnt sugar, rock candy, toffee, and slight coffee. Also, crystallization of the simple sugars produced during saccharification lends added complexity to these malts.
Roasted barley or malt:
Roast Barley, Black Patent, Chocolate
Roasted malts are made by heating the grain at high temperatures for long periods. This is very similar to the roasting of coffee beans. Roasting creates compounds at the far end of browning that lend very dark colors; burnt aromas; bitter, burnt, and acidic tastes; and even acrid astringency. At first glance these don’t sound tempting, but they are the key malt attributes found in stouts, porters, and other dark beers.
Beside browning, malt flavor can arise from two other compounds: dimethyl sulfide, commonly referred to as DMS, and tannins.
Dimethyl sulfide is a volatile oil. In a relatively low concentration, below 100 parts per billion, it contributes a desirable aroma and taste to lager beer. Above this concentration it becomes offensive, and terms such as “cooked corn,” “tomato ketchup,” and “parsnip-like” are used to describe its aroma.
The consensus in the brewing science literature is that all the DMS in beer arises from a precursor in malt produced during germination and the early, low-temperature part of kilning. This precursor, S-methyl methionine (SMM), is directly converted to DMS when it is heated during kilning. Since DMS is volatile, it becomes a gas and is driven off during kilning. If sufficient heat is added, the DMS will convert even further to a non-volatile compound called dimethyl sulfoxide (DMSO).
The level of SMM in malt can vary due to environment factors and the varietal of barley used. Six-row varieties tend to have higher SMM than two-row varieties. Lots of nitrogen in the soil increases levels of SMM, and high germination temperature increases it as well.
Production of DMS does not occur only at the malt house; much of the precursor is converted to DMS in the brewhouse. The high temperatures of mashing, lautering, and especially boiling all can convert SMM into volatile DMS.
Boiling drives off most of the DMS. However, there are two ways in which DMS can arrive in the fermenter. The first is by formation in the fermenter: a portion of the DMS turns into DMSO during the boil, which is not volatile like DMS (it doesn’t become a gas and disappear into the atmosphere), and so it is carried into the fermenter. There, yeast will convert it back to DMS.
The second way is by being carried directly into the fermenter. If the wort is held hot for an extended period of time after the boil, DMS production will continue due to the heat, but it will not be driven out of solution as rapidly as during the boil. Therefore, it gradually builds up in the wort. This is especially true if the hot wort is in a closed container. During fermentation, carbon dioxide production will carry away a good portion of the DMS.
As a homebrewer, you can’t control the amount of the precursor SMM in malt. However, you can choose malts that will yield varying levels of DMS in beer. You can also manipulate the wort boil to alter beer DMS levels.
In general, very pale malts have a greater chance of yielding high-DMS beers than higher kilned malts. The classic comparison is between lager malt and ale malt. Since ale malts are kilned at higher temperatures than lager malts, they produce beers with less DMS than lager malts. Regarding the boil, experimenting with the length of the boil and the degree of evaporation, as well as the length of time the wort is held hot during trub settling (wort clarification) will allow a degree of manipulation of the DMS levels in the final product.
Tannins
Tannin is a general term historically used for the dark, astringent extract of vegetable matter used in the tanning process. Maltsters and brewers refer to certain materials of the malt husk as tannins. The major flavor contribution from tannins is astringency. When extracted in very hot water, husk tannins can lend astringency to beer. The same extraction process occurs when you steep tea leaves in hot water.
Typically, astringency is not a problem as long as sparge water temperatures are not excessive. Most brewers prefer sparge water between 165˚ F and 170˚ F, though some brewers approach 180˚ F to increase runoff rate. Another potential contribution of tannins is on visual impact; they can cause haze (polyphenol-protein complexes). Since most homebrewers do not filter their beer, this is not a major problem.
Smoked Malt
Smoked malts used in the brewing of beer use woods such as beech, apple, alder, and ash to fire the kiln. The smoked malts are not kilned to the point where the kernels themselves begin to smoke; all good smoked malts look hardly distinguishable from Munich malt (until you smell them).
Some brewers also use peat to fire the kiln. Traditionally, peat malt is used in Scotch whiskey. In general, peated malts produce very assertive flavors in beer; the medicinal flavors they contribute are too strong for many beer drinkers, even in small additions.
The smoked malts made using beechwood or the like can make fine beers, even when the grist bill is 100 percent smoked malt. However, with any such malt care must be taken to balance the smoked flavor so that the beer does not taste as if you just swallowed a pint of liquid smoke.
The best way to learn about malt flavors and their effect on your beer is to experiment and observe carefully. If you have an adventurous spirit you will build, over time, a familiarity with specialty malts that can only make tasting and discussing beer more enjoyable. This familiarity with the various malts is a powerful tool in unlocking creativity in the brewing process.
